The present application relates to a semiconductor device having a contact pattern used for connecting n (where notation n denotes a positive integer at least equal to three) conductive layers to each other, a method for manufacturing the semiconductor device and display apparatus to which the semiconductor device can be applied. Examples of the display apparatus are a liquid-crystal display apparatus and an organic EL (electro luminescence) display apparatus.
In recent years, the popularization of portable terminals such as hand-held phones and PDAs (Personal Digital Assistants) is amazing. The portable terminals are being rapidly popularized by, among others, the availability of the liquid-crystal display apparatus each employable in the portable terminal as an output display section. This is because, in principle, the liquid-crystal display apparatus has a characteristic of requiring no driving power. That is to say, the liquid-crystal display apparatus is a display apparatus having small power consumption.
The contemporary active-matrix display apparatus making use of polysilicon TFTs (Thin Film Transistors) as pixel switching devices has a tendency to integrate a pixel display area section composed of pixels arranged in the form of a matrix and digital interface driving circuits into a single unit on the same substrate.
To put it in detail, in this display apparatus integrating the digital interface driving circuits with the pixel display area section into a single unit, a horizontal driving system and a vertical driving system which compose the digital interface driving circuits are provided in the peripheral parts of an effective display portion of the pixel display area section. The driving systems making use of polysilicon TFTs are integrated with the pixel display area section into a single unit on the same substrate.
In addition, in recent years, the liquid-crystal display apparatus and the organic EL display apparatus which are employed in hand-held phones or the like are desired to have a small size and a small weight even though the display apparatus itself has a high-resolution and large screen of the three-inch WVGA (Wide Video Graphics Array) class.
Some of the liquid-crystal display apparatus and the organic EL display apparatus are display apparatus each making use of the amorphous silicon (a-Si) material used for making a semiconductor layer. In the case of such a display apparatus, it is necessary to implement the driving circuits as silicon (Si) chips in the peripheral parts of an effective display portion of the pixel display area section employed in the display apparatus. In consequence, it is inconvenient to reduce the size of the pixel display area section employed in the display apparatus and/or narrow an area occupied by the peripheral parts of the effective display portion of the pixel display area section.
As a method for solving the above problem, there is also provided a method for producing the display apparatus described above. In accordance with this method, the driving circuits are created in a process carried out at the same time as the process to form pixel transistors on a glass substrate. The driving circuits are created on the same glass substrate by making use of a semiconductor layer having a mobility greater than that of an amorphous silicon film. Examples of such a semiconductor layer are a low-temperature polysilicon film, a microcrystal silicon film and an oxide semiconductor film.